Field of the Invention
The present invention relates to an inkjet printing apparatus and a check pattern printing method, and more particularly, to a technique of adjusting the print position of a clear ink having no coloring material which is to be applied to a print medium together with coloring material inks to perform printing.
Description of the Related Art
Use of a clear ink together with coloring material inks can improve the fastness of a printed object and can increase a printing density (OD). There is known a technique of printing a check pattern for checking a state of ejection in order to adjust ejection of the clear ink.
For example, as patterns used for adjusting the print position of the clear ink, Japanese Patent Laid-Open No. 2000-141624 discloses printing several patterns in which the relative print position of the clear ink is shifted from that of the coloring material inks. The color of a pattern formed by the coloring material inks in a case where the patterns of the two inks overlap each other is different from the color of a pattern formed by the coloring material inks in a case where the patterns of the two inks do not overlap each other, and by using this feature, the print position shift amount of the clear ink is detected, and the print position is adjusted based on the detected shift amount.
Further, as a technique of checking the state of ejection of the clear ink, Japanese Patent Laid-Open No. 2005-22216 discloses printing the coloring material inks so as to overlap the clear ink at the time of printing a pattern for checking the state of ejection of the clear ink. In an area in which the clear ink is ejected satisfactorily, a chance in density occurs due to overlapping of the coloring material inks, and by detecting this change, the state of ejection of the clear ink is checked.
Furthermore, in a print head for ejecting the clear ink as in the case of the coloring material inks, the amount of ejection may vary depending on a nozzle because variations in the print head arise at the time of manufacturing and the print head changes over time. In order to overcome this problem, so-called head shading (HS) correction, which is well known for the coloring material inks, is performed to adjust the applying amount of the clear ink. In the case of performing the HS correction, the clear ink is ejected to print an HS pattern. It is desirable that this pattern make it possible to detect a difference in density which varies depending on the applying amount of the clear ink riot including the coloring material. Regarding the HS pattern, Japanese Patent Laid-Open No. 2005-22216 discloses a technique of detecting a change in density caused by applying the clear ink as described above.
However, in the technique disclosed in Japanese Patent Laid-Open No. 2000-141624, there is a case where the amount of change in color is relatively small between an area in which the coloring material inks and the clear ink overlap each other and an area in which the coloring material inks and the clear ink do not overlap each other. In this case, a shift of the print position cannot be detected satisfactorily, and as a result, high-accuracy adjustment of the print position cannot be performed. Further, in the technique disclosed in Japanese Patent Laid-Open No. 2005-22216, there is a case where the amount of chance in density or color is small between the area in which the clear ink and the coloring material inks overlap each other and an area in which only the coloring material inks are printed. In this case, it is difficult to check the state of ejection with high accuracy. For example, in a case where the coloring material inks have properties such that the coloring material inks are likely to remain in an upper layer of a print medium, or in a case where a print medium itself has properties such that the coloring material inks are not likely to permeate the print medium, the amount of change in density or color is small between a case where the clear ink overlaps the coloring material inks and a case where the clear ink does not overlap the coloring material inks. Further, even in a case where the technique disclosed in Japanese Patent Laid-Open No. 2005-22216 is used to print the pattern for HS (correction of the amount of application), a sufficient change in density for detecting a difference in the applying amount of the clear ink may not be obtained depending on a combination of the kind of print medium to be printed with the pattern and the inks. As a result, there is a case where it is impossible to correct the amount of application with high accuracy.
In this manner, in the case of printing the check pattern for adjusting ejection of the clear ink, the conventional technique has a problem that even in a case where the coloring material inks are printed to overlap the clear ink in order to detect a change in color or density, a sufficient difference in color or density cannot be obtained between the area in which the clear ink is printed and the area in which the clear ink is not printed.